The major research objective has been elucidation of basic mechanisms controlling carbohydrate metabolism in normal and in cancer cells. Recently these studies have focused on the number, distribution and properties of the isozymes of pyruvate kinase. At least three noninterconvertible pyrivate kinases have been found, one which predominates during fetal life and two which develop at birth. These isozymes have been shown to be regulated differently and to have distinct physical properties. At present a major effort is being made to compare the structures of these enzymes in order to definitely prove they are the products of distinct genes and to take advantage of the fact that the isozymes represent evolutionary analogues which have similar catalytic properties. That is: differences in structure should have a high probability of relating to differences in the mechanism of control and to physiological function. Also under study are the mechanisms which account for the switch in the isozyme pattern. Neoplasms tend to revert back to the fetal type of isozyme. Moreover, extracts of tumors injected into otherwise normal mice induce a similar switch in liver tissue. The factor responsible appears to be a polypeptide. Presently studies are being conducted to better characterize the structure and mode of action of this factor. In an attempt to develop an in vitro essay system various cultured cell lines have been assayed in order to find a line having a differentiated form of the enzyme. Surprisingly LMTK minus cells appear to have a fourth isozyme. At present the relationship of this enzyme to the others and the effect of this factor on synthesis or degradation of these enzymes are under investigation.